Polycarbonates are useful in the manufacture of articles and components for a wide range of applications, from automotive parts to electronic appliances. Because of their broad use, particularly in metal replacement applications, such as in automotive applications, there is a need for increased stiffness and reduced coefficient of thermal expansion of the materials, while at the same time maintaining their excellent ductility and flow properties.
One known method of increasing stiffness in polycarbonates is by the addition of inorganic particulate fillers such as clay, talc, and mica. However, the use of such fillers presents some drawbacks. Talc- and/or mica-filled polycarbonates and polycarbonate blends, can degrade upon processing. The degradation of polycarbonates and/or polycarbonate blends is known to the skilled practitioner and generally refers to a reduction in molecular weight and/or an adverse change in mechanical or physical properties. For example, the addition of these inorganic particulate fillers has been observed to affect the ductility and/or flow of polycarbonates and polycarbonate blends. Finally, the use of talc can give rise to poor stress transfer at the polymer-talc interface, leading to a reduction in tensile and flexural properties.
Various filler treatments intended to address the above drawbacks have been developed, including treatment with acid (see, e.g., US Publication No. 2006/0287422) and various substituted silanes (U.S. Pat. No. 5,637,643). However, neither the acid nor the silane treatments tested have been found to counter the adverse impact of talc on ductility or flow properties when added to polycarbonate blends, particularly with acrylonitrile-butadiene-styrene. Moreover, in some instances, the use of talcs treated with aminosilane coupling agents provides compositions with even less favorable properties, due to the degradation of the compositions mediated by the relative alkalinity of the amine moieties on the talc surface. In an alternative approach to improving the ductility of polymer-filler compositions, there are also reports of rubber particle encapsulation in the polymer matrix. However, doing so comes at the cost of reduced tensile and flexural properties.
Thus, there is a need for eliminating filler-induced polymer degradation in polycarbonate thermoplastic compositions, while at the same time improving the ductility and flow properties of these polycarbonate blends.